Hot Plane Strain Compression Research Articles

Interpretation of hot plane strain compression testing of aluminium specimens

Plane strain compression (PSC) testing is now generally accepted as one of the most reliable methods for the generation of flow stress data and microstructural investigation of thermomechanical processing. It has been known for some time that extremely reproducible measurements may be made across different laboratories if a standardised procedure is used. However, particular care must be taken with both the experimental procedure and the interpretation of the measured force–displacement data. The present paper reports investigations that have built on previous work and looked further at the effects of spread of the specimen and friction. In deriving reliable flow stress data, the importance of tool and specimen geometry and consideration of the effects of lubrication and friction are clearly demonstrated. Furthermore, the paper demonstrates the current status of the work by presenting the algorithms behind new software that has been developed for interpretation of raw force–displacement data in a logical and consistent way.

Nucleation and growth of recrystallisation in Al–1Mg during thermomechanical processing

A procedure based on quantitative optical microscopy has been used to investigate nucleation and growth of recrystallisation in an Al–1Mg alloy. Hot rolling and plane strain compression tests were employed for this purpose, providing strains within the range 0·2–2·2 and strain rates within the range 2·5–4·9 s-1, while annealing was carried out at 400°C in all cases. The nucleation kinetics is not site saturated, particularly at low strains, the major discrepancy being observed early during recrystallisaton. However, in practice site saturation is a reasonable approximation. During recrystallisation, the average growth rate decreases continuously. Although concurrent recovery in the unrecrystallised fraction is expected to lead to a decrease in growth rate, the magnitude of the reduction is such that a non-uniform distribution in stored energy is expected to play a significant role.

Macroscopic and microscopic subdivison of a cold–rolled aluminium single crystal of cubic orientation

An aluminium single crystal of cube orientation has been rolled to 15, 30 and 50% reductions under controlled homogeneous rolling conditions. The deformation structure of the rolled specimens was investigated by both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) over several scales of magnification. The local crystallographic orientations have been measured by an automatic electron back scattering patterns (EBSP) technique and a semiautomatic TEM method. Orientation image maps based on the local orientation data have been used to reveal the evolution of the deformation structure during rolling. It is observed that by an opposite rotation around transverse direction (TD) the crystal was subdivided into four macroscopic bands, termed matrix bands in the present paper, which are parallel to the rolling plane. Between the four bands there are three transition bands in which the orientation changes continuously from that of a matrix band to that of the adjoining one. A model based on the idea of location–dependent shear strain caused by geometric and friction effects together with a plasticity analysis has been used to explain the macroscopic subdivision of the crystal. In addition to the macroscopic subdivision, a microscopic subdivision by the formation of cell–blocks within the matrix bands and a cell structure within transition bands has also been observed. A difference related to shear amplitude difference between the active slip systems changing continuously across the crystal has been observed. Both the macroscopic orientation of the dislocation boundaries and the misorientation angles and axes across dislocation boundaries are analysed and it is found that Frank9s formula is a useful tool in analysing the dislocation boundaries formed during deformation.

Constitutive equations for high temperature flow stress of aluminium alloys

Constitutive equations for the relationship between stress, strain, strain rate, and temperature are an essential input for modelling thermomechanical processing. Hot plane strain compression testing was used to deform commercial purity aluminium, Al-1Mn, and Al-1Mg alloys at temperatures of 300, 400, and 500°C and equivalent strain rates of 0.25, 2.5, and 25 s−1, to an equivalent strain of 2. Flow stress data obtained from these tests were analysed using the Sah et al. and hyperbolic sine forms of relationships. Values of constants in the constitutive equations were obtained and were shown to provide an accurate description of the experimental stress-strain curves, including the effect of temperature rise due to deformational heating and the effect of changing strain rate. The application and limitations of the relationships are discussed.

Constitutive equations for high temperature flow stress of aluminium alloys

Constitutive equations for the relationship between stress, strain, strain rate, and temperature are an essential input for modelling thermomechanical processing. Hot plane strain compression testing was used to deform commercial purity aluminium, Al-1Mn, and Al-1Mg alloys at temperatures of 300, 400, and 500°C and equivalent strain rates of 0.25, 2.5, and 25 s−1, to an equivalent strain of 2. Flow stress data obtained from these tests were analysed using the Sah et al. and hyperbolic sine forms of relationships. Values of constants in the constitutive equations were obtained and were shown to provide an accurate description of the experimental stress-strain curves, including the effect of temperature rise due to deformational heating and the effect of changing strain rate. The application and limitations of the relationships are discussed.

Ajuste de las curvas tensión-deformación a alta temperatura de un acero microaleado Nb-Ti

A series of hot plane strain compression tests have been conducted on a Nb-Ti microalloyed steel in a Servotest machine on samples of approx. 10 mm in thickness. Two sets of tests at strain rates of 5 s-1 and 15 s-1 were used and monitored the stress-strain behavior at deformation temperatures varying from 850 to 1,025 °C. The experimental data were corrected for friction, deviation from plane strain compression (PSC) conditions and adiabatic rise of temperature, to give the isothermal equivalent tensile stress-strain curves. Thereafter these curves have been modeled by two types of equations depending on the softening mechanism operating during the deformation process and calculated the value of the coefficients in the equation by the application of a Taylor series around an initial point close to the solution. Finally, by the application of the least squared method, the previous values are compared to the experimental ones in order to determine an optimized value of the coefficients in the equations which model the stress-strain behaviour of the steel.

Hot Plane Strain Compression Testing of Aluminum Alloys

Abstract Plane strain compression is a versatile laboratory testing method for simulating industrial hot working operations such as plate and strip rolling. The deformation can be closely controlled to the required conditions of temperature and strain rate, and high strains can be achieved without instability. However, for accurate determination of flow stress, care must be taken with experimental procedure and the interpretation of the measured force-displacement data. This paper reports the results of work carried out in three laboratories on samples of the same cast of Al-1% Mn alloy. In particular, the effects of spread and friction are analyzed as a function of initial specimen geometry. When consistent procedures are used it is shown that excellent reproducibility of flow stress data is obtained between laboratories. In deriving constitutive relationships, the importance of considering the effects of lubricant films, of deformational heating, and of heat transfer are clearly demonstrated.

Microstructural analysis of steel–nickel alloy clad interfaces

The microstructures obtained by diffusion bonding a low alloy steel AISI 4130 to nickel alloys (Inconel 625 and Hastelloy G3), using different techniques (hot uniaxial pressing, hot plane strain compression, hot isostatic pressing (hipping), and coextrusion) have been studied by light microscopy, scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM). The interdiffusion of various elements through the interface has been determined using microanalysis in both the SEM and the STEM. In all instances profuse precipitation of M23C6 carbides, resulting from the diffusion of carbon from the steel into the superalloy, is clearly visible in a region close to the interface on the superalloy side. For specimens processed by hot pressing and coextrusion, this region shows a work hardened substructure composed of cells and dislocations. By contrast, in specimens processed by hipping a poorly developed substructure, with few dislocations associated with grain boundaries and carbides, is observed. The thickness of the precipitation region increases with increasing temperature and bonding time. Carbides precipitate preferentially at the grain and twin boundaries, although for the higher temperatures used in hipping, the precipitation inside the grains is also important. On the steel side, a precipitation free austenite band is observed in all specimens analysed. This band is the result of the diffusion of nickel and chromium from the superalloy to the steel, thus stabilising austenite at room temperature. From the experimental concentration profiles of different elements, the corresponding diffusion coefficients have been calculated using diffusion theory, and compared with data reported in the literature. Good agreement between these data and the experimental values can be observed.MST/3200

Modelling the plane strain compression test to obtain constitutive equations of aluminium alloys

Hot plane strain compression tests on 1050, 1198, 3003 and 3004 aluminium alloys have been conducted. Based on these experiments and on a set of internal type constitutive equations for hot working, the values of the parameters in the constitutive functions are determined. The constitutive equations proposed here, with the constitutive functions and material parameters associated, accurately reproduce the basic tests. The procedure used to fit the material parameters is improved, in comparison with classical slip line analysis, by using a finite element modelling of the plane strain compression test. It is demonstrated that accurate plane strain or three-dimensional large strain finite element analysis can be used to correct the friction and lateral spread effects. Furthermore, it is demonstrated from comparison with the experimental observations that microstructural parameters can be accurately determined from numerical modelling. The constitutive equations and finite element procedure proposed here can be useful for obtaining an improved analysis of hot rolling of aluminium alloys.

Confirming mathematical metalworking models by comparison with microstructures

AbstractReference microstructures produced from hot plane strain compression tests have been compared with as extruded microstructures for a powdered aluminium 2014 alloy. This comparison enables an independent check to be made of a mathematical model of the changes in billet temperature during extrusion, which are difficult to monitor experimentally. Powder product microstructures that are more uniform than those produced from equivalent solid feedstock have been attributed to a narrower process temperature range even though the same range of billet temperatures was used. Within this range microstructural changes have been related to those in reference samples produced under closely controlled test conditions.MST/2004

Annealing Textures in Aluminium Deformed by Hot Plane Strain Compression

Annealing Textures in Aluminium Deformed by Hot Plane Strain Compression

Texture Development in Al 3003 during Hot Plane Strain Compression

Texture Development in Al 3003 during Hot Plane Strain Compression

Hot plane strain compression testing of partially consolidated powder compacts: H. Shi and A. Greasley (University of Sheffield, UK), Powder Metallurgy, Vol 35, No 4, 1992, 269–274

Hot plane strain compression testing of partially consolidated powder compacts: H. Shi and A. Greasley (University of Sheffield, UK), Powder Metallurgy, Vol 35, No 4, 1992, 269–274

Microstructural Development During Hot Working of Powdered Aluminium Alloy

Microstructural analysis of quenched hot plane strain compression specimens has revealed key temperatures, strain levels, and strain rates in the development of the microstructure of compacted aluminium 2014 powder. The removal of the rapidly quenched cast microstructure in the powder feedstock, the obliteration of prior powder particle boundaries, the onset of both partial and complete recrystallisation, and the beginning of hot shortness have been categorised in terms of critical temperatures, strains, and strain rates. It has been shown that restoration processes can produce non;uniform microstructures unless certain strain rates are achieved

Hot Plane Strain Compression Testing of Partially Consolidated Powder Compacts

Hot plane strain compression testing is shown to be more suitable than hot torsion testing in providing flow stress data for partially consolidated aluminium 2014 powder which forms the matrix of many advanced composites. It is demonstrated that data provided by this technique are comparable to hot torsion data by the use of a solid control alloy. Activation energies and constitutive equation constants are derived from the data for use in analytical process models. It is proposed that this method of testing provides an extremely useful way of monitoring the flow behaviour of powder based materials that are not amenable to other test methods

Influence of changing strain rate on microstructure during hot deformation

Hot plane strain compression tests have been carried out on a ferritic stainless steel, commercial purity aluminium and an aluminium 1% magnesium alloy under conditions of constant strain rate and with strain rate changed in a controlled manner from one constant value to another. At constant strain rate, subgrain size and dislocation density inside subgrains are related to flow stress in the manner observed previously on other materials. During and after changes in strain rate, subgrain size and dislocation density are not uniquely related to flow stress. Significant strain intervals after a strain rate change are required to establish the new equilibrium subgrain size. For the alloys, these strain intervals are larger when strain rate is increased than when it is decreased. The opposite is found for the commercial aluminium. This difference in behaviour is explained In terms of the relative rates of glide and climb of dislocations.